There is a bug that lets you get back on the horse directly from the floor. It shouldn't happen, but it does under a specific condition.
Been so used to controlling 1 block movable objects that this took me a while even if I knew what to do. Keep making these kinds of levels for me~!
Spoiler: Getting back on the horse it is possible to get back on the horse directly from the floor. You simply need to move the horse to an area on the screen that allows you to tap on the block, or the rail, and NOT get a red X. Really!